99% Memory usage + extreme lag when building UE4 from source

As the title suggests, I’m trying to build UE4 4.26 from source, following these steps: Building Unreal Engine from Source | Unreal Engine Documentation

Pretty soon after pressing ‘build’, my PC’s RAM usage shoots up to 99% which makes my computer virtually unusable due to the extreme lag/delay on performing any action at all… Which is fine, except for the fact that I the build itself takes well over an hour (probably more like a couple hours, I haven’t actually timed it) even on decent hardware:

My PC specs are: (which I believe are sufficient)

  • AMD Ryzen 7 3700X
  • GTX 3070
  • 16GB 3200MHz DDR4 RAM (2 x 8GB Modules)
  • Corsair RM750 (750W PSU)
  • Gigabyte B450M Aorus Elite Motherboard

Windows is installed on a SSD, and Visual Studio 2017/2019 is installed on an NVMe. (albeit I’ve tried it with VS installed on the same drive as Windows as well, with no real difference)

Given the build is taking as long as it is, and my RAM usage renders my PC almost unusable to the point where I can barely even click ‘cancel’ on the build, is something wrong? Or is 2+ hour build times and EXTREME lag a normal thing?

Thank you kindly for any help!